The invention relates to a vehicle having an electrical system, which electrical system comprises a first partial electrical system having a first energy store of a first nominal voltage level, a second partial electrical system having a second energy store of a second nominal voltage level and a DC-DC converter between the two partial electrical systems.
In particular, vehicles with an electric drive train usually have a plurality of electrical energy stores in partial electrical systems of varying voltage levels. A DC-DC converter establishes an electrical coupling between the partial electrical systems. This can be seen, for example, from the document WO/2011/009673 A1.
An object of the invention is to describe an improved vehicle having an electrical system, which electrical system comprises a first partial electrical system having a first energy store of a first nominal voltage level, a second partial electrical system having a second energy store of a second nominal voltage level and a DC-DC converter between the two partial electrical systems.
According to one embodiment of the invention, the first energy store comprises a housing which has at least a first tap for the first nominal voltage level, by means of which the first DC-DC converter can be electrically supplied, and at least a second tap for the second nominal voltage level, by means of which the second energy store can be electrically supplied, wherein the at least one first tap and the at least one second tap are galvanically isolated, the housing contains a voltage conversion unit, and electric voltage of the first nominal voltage level can be substantially converted into voltage of the second nominal voltage level by the voltage conversion unit.
For example, the vehicle has a high-voltage store which comprises as an essential component an electrochemical high-voltage battery as a first energy store. The high-voltage store is characterized by a housing closed outwardly therefrom having at least two taps which are accessible from the outside.
It is especially advantageous if the housing has at least one contactor contact, through which a first contactor position can be occupied and a second contactor position can be occupied, in the first contactor position the at least one tap can be switched in a de-energized state, in the second contactor position an electrical voltage drops across the at least first tap, an electrical voltage can be applied by means of the voltage conversion unit in the first contactor position across the at least second tap, and an electrical voltage can be applied by means of the voltage conversion unit in the second contactor position across the at least second tap.
This means that the voltage conversion unit comprises a permanent electrical connection with the high-voltage battery within the housing of the high-voltage store independent from a switch position of the contactor contact. In contrast, the electrical connection between the high-voltage battery and the first tap can be switched by means of the at least one contactor contact.
According to a preferred embodiment of the invention, the second partial electrical system comprises electrical consumers of the second nominal voltage level, and the electrical consumers can be electrically supplied via the second tap.
The voltage conversion unit thus converts electrical power from the voltage level of the high-voltage battery to electrical power of the voltage level of the second energy store, and makes this available at the second tap. The second energy store is suitably designed as a power-optimized energy store, i.e. has a high charge acceptance ability. By means of example, in addition to a secondary store, a supercapacitor unit also comes into consideration here, which can thus be charged from the high-voltage store via the second tap. For charging, electrochemical overpotential can be set by the voltage conversion unit at the supercapacitor unit, in order to charge it. This means that the supplied voltage of the second nominal voltage level exceeds this overpotential. In this context, the voltage conversion unit “substantially” sets the voltage at the second nominal voltage level.
Furthermore, it is useful if the second tap is assigned a comparator circuit, a switch-on signal can be transmitted to the voltage conversion unit via the comparator circuit, and a switch-off signal can be transmitted to the voltage conversion unit via the comparator circuit.
The comparator circuit is assigned a first switching voltage value and a second switching voltage value, so that a voltage dropping across the second tap can be compared with the first switching voltage value and with the second voltage switching value via the comparator circuit.
Via the comparator circuit, the switch-on signal can be transmitted across the second tap in the case of a dropping voltage which is lower than the first switching voltage value, and the switch-off signal can be transmitted across the second tap in the case of a dropping voltage which exceeds the second switching voltage value.
Via the comparator circuit, the voltage conversion unit can thus be switched on and off according to a voltage hysteresis applied to the second tap.
The first nominal voltage level is preferably in a voltage range of 12 volts to 600 volts, and the second nominal voltage level in a voltage range of 12 volts to 60 volts.
It is further useful if the voltage conversion unit has a nominal output power, and the nominal output power substantially corresponds to a typical power requirement of the second partial electrical system in a stationary operation of the vehicle.
The stationary operation of the vehicle is to be distinguished from a driving operation and an idling state of the vehicle. In contrast to stationary operation, dynamic driving maneuvers are performed in the driving operation of the vehicle. This means that a charging operation of the vehicle, in which the high-voltage store is charged, for example by cable at a charging station, represents a sub-case of stationary operation. During driving operation and stationary operation, the vehicle is operationally active. The idling state of the vehicle must here be distinguished, in which the vehicle is not operating.
The invention is based on the considerations set out below:
Vehicles exist which have a plurality of energy stores, such as plug-in hybrid vehicles (PHEV), hybrid vehicles (HEV), electric vehicles (BEV) and vehicles with an engine start-stop function. All of these vehicles have a need for idle current in non-operational states, which generally burdens the energy stores.
In the case of vehicles with an electric drive train, an increased idle current and current in stationary operation are further generated through the charging of a high-voltage energy store. This usually requires a stationary or cyclical recharging of a low-voltage battery via a central DC/DC converter in an inefficient partial load operation thereof.
The need of the vehicle for idle current leads to a strong discharge of a central 12-volt lead-acid battery, which is used, of course, as a low-voltage battery, and which is thereby partially discharged after a stationary phase and idling phase and is thus prematurely aged. Consequently, this lead-acid battery is to be designed correspondingly with premature aging and dimensioned with high capacity.
In electric vehicles, recharging of the lead-acid battery in the stationary and idling phases is generally carried out by the DC/DC converter, which usually has a very poor working efficiency (i.e. <<75%), in the region of <<10 amps, in the currents to be delivered in this operation, and therefore causes high electrical losses. This has a negative effect on charging efficiency and thus also the energy and pollutant balance of the vehicle.
It is proposed to ensure an energy-efficient optimized supply of idling and stationary current in the electrical system to the low-voltage battery by means of a specially mounted, high-efficiency low-voltage tap on the high-voltage store. This is used to recharge the low-voltage battery and to supply the active logic of the control devices of the vehicle.
This has the consequence that in the idling state of the vehicle, in stationary operation and during the charging phase, the lead-acid battery is not discharged and thus can be designed with a weak capacity, i.e. a smaller lead-acid battery can be used than without the tap.
Alternatively, a lithium battery or a supercapacitor can be used. The DC/DC converter is not required to recharge the 12-volt lead-acid battery, and power loss is avoided. Thus, there is an increased electrical efficiency of the vehicle and an improved pollutant balance due to weight-saving and an improved energy efficiency. Furthermore, the probability of failure of the low-voltage battery is effectively suppressed.
The low-voltage tap is realized through a voltage conversion unit. The integration of the voltage conversion unit occurs advantageously within the housing of the high-voltage store, to avoid costly high-voltage cabling outside the store. In terms of circuitry, the input-side terminal of the voltage conversion unit on the high-voltage store is independent of the switching position of a high-voltage contactor or of the high-voltage contactor at the potential of a high-voltage battery of the high-voltage store, i.e. within the pole of the high-voltage battery. The high-voltage contactors or the high-voltage contactor is normally open in stationary operation and in an idling state.
Hereafter will be described with reference to the accompanying drawings an exemplary embodiment of the invention. Further details, preferred embodiments and developments of the invention result therefrom. Individually schematically shown are
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.